The invention relates to an image recording method in which a charge pattern is directly formed on a toner layer of a donor by utilizing a multi-stylus electrode, which toner layer is subsequently transferred onto a transfer sheet to produce an image, and an apparatus used for carrying out the method.
A recording method is known in the prior art in which an image signal is applied to a multi-stylus electrode for selectively charging or discharging the surface of a latent image carrier to form an electrostatic latent image in accordance with the image signal, which is then converted into a visual image by the use of toner which can be transferred onto a record sheet. The known method suffers from the problem which results from the fact that the multi-stylus electrode is disposed in contact with or in the close vicinity of the surface of the latent image carrier. If any toner remaining after the transfer step of a preceding operation is deposited on the multi-stylus electrode, the recorded image can be adversely influenced. Hence, it is necessary that the latent image carrier be sufficiently cleaned after the transfer of the visual image. However, a satisfactory cleaning operation is usually difficult to achieve if the carrier is to have a prolonged life.
A recording method has been proposed to avoid such problem, and utilizes a counter electrode, referred to as a donor, which has its surface covered with a toner and which is disposed in opposing relationship with the multi-stylus electrode with a given small gap therebetween. A record sheet is passed between these electrodes while applying an image signal to the multi-stylus electrode, thus producing a local electric field extending through the record sheet in accordance with the image signal. The electric field acts to transfer the toner from the donor onto the surface of the record sheet, thereby forming a visual image thereon. With this method, contamination of the multi-stylus electrode by the toner is avoided because of the presence of the record sheet between the donor and the multi-stylus electrode. However, this method suffers from the problem that the sharpness of the visual image may be degraded depending on the thickness of the record sheet since the multi-stylus electrode is located on the rear side thereof. In addition, the multi-stylus electrode is subject to a discharge, generally a spark discharge, which causes an erosion of the electrode, thus preventing its use over a prolonged period of time.
To cope with this problem, the present inventor has previously proposed a recording method comprising the steps of uniformly forming a thin toner layer, having an increased resistivity to maintain the charge thereon, on the surface of a moving donor member, disposing a multi-stylus electrode to which a pattern signal is applied in contact with the toner layer to form a charge pattern in accordance with the pattern signal, and then disposing a record medium in superimposed relationship with the toner layer to transfer the toner according to the charge pattern onto the record medium. In this earlier invention, the steps of forming the thin toner layer uniformly on the surface of the donor member can be achieved by resiliently urging a metal doctor against the surface of the donor member which itself has a certain resilience. However, with this technique, it is difficult to produce a uniform pressure between the surface of the donor member and the doctor, resulting in a number of drawbacks including the failure of forming a uniform thickness of the toner layer, non-uniformity in the optical density of the transferred image, and the generation of undesirable stresses produced in the toner as a result of the pressure between the donor member and the doctor under a force of friction applied by the doctor to cause a fracture of toner during a prolonged period of use or a solid adherence of toner to the surface of the donor member, producing abnormalities in a transferred image.